Oxygen is typically a stable substance referred to as triplet oxygen in the atmosphere. If a portion of that oxygen changes to a highly reactive substance referred to as active oxygen such as superoxide, hydroxy radical, singlet oxygen or hydrogen peroxide in the body, a portion of the substance fulfills the role of a biodefense mechanism against foreign substances produced by neutrophils and macrophages, while on the other hand, if the active oxygen is present in excess in the body, it has been clearly demonstrated to attack lipids, proteins, enzymes, nucleic acids or the like, resulting in damage to biomembranes, tissues and the like and causing arteriosclerosis, cerebrovascular disorders, pulmonary emphysema, rheumatoid arthritis, cataract, hypertension, senile dementia, Alzheimer's disease, or the occurrence of blotches and freckles, aging or the like.
In order to prevent the above various conditions caused by oxidative stress attributable to this excess active oxygen, a wide range of searches have been made for antioxidative substances whereby superoxide dismutase (SOD)-like substances having a function similar to that of SOD, which is an enzyme that catalyzes a reaction producing hydrogen peroxide and oxygen molecules by disproportionation of superoxide (O2−) that is a starting substance, and substances scavenging active oxygen (substances having active oxygen removing activity) are added to feeds.
For example, such substances include as a naturally-occurring substance liposoluble α-tocopherol (vitamin E) and water-soluble ascorbic acid (vitamin C), and as a synthetic substance phenolic substances such as butylhydroxytoluene (BHT), butylhydroxyanisole (BHA) and tertiary-butylhydroquinone (TBHQ).
However, although these substances are typically used as antioxidative substances in foods, their action in removing active oxygen from the body is inadequate and they have also been associated with problems, such as the synthetic substance, BHA, being suspected of possessing carcinogenicity.
Therefore, considerable research and development has been conducted in recent years to find an extremely safe active oxygen remover from natural sources such as animals and plants, and examples of such substances are disclosed in Patent Documents 1, 2, 3, 4 and 5. In addition, as for substances that have actually been commercialized, polyphenol-based compounds such as catechins extracted from tea leaves and cocoa bean extract, anthocyanin-based compounds contained in blueberry skin, and isoflavones obtained from fermented soy beans have attracted particular attention due to their extremely high level of active oxygen removal effects.
Among these polyphenol-based compounds that have been clearly demonstrated to have high active oxygen removal effects, catechins contained in tea leaves have been determined to demonstrate higher active oxygen removal effects than the other polyphenols, which catechins are flavanols having as a basic skeleton flavan-3-ol such as (−)epigallocatechin, (−)epigallocatechin-3-gallate, (−) epicatechin, (−)epicatechin-3-gallate and (+)catechin.
On the other hand, tannin, which is extracted with water from bark of an Acacia species, scientific name: Acacia mearnsii De Wild., has long been produced in large quantities in South Africa and Brazil. It is typically referred to as “wattle tannin”, and is used inexpensively mainly as a tanning agent or in wood adhesives. In addition, since scientific name: Acacia mangium Willd. (acacia mangium) grows extremely rapidly, it has recently been planted extensively in subtropical and tropical regions such as in Indonesia and Malaysia. This wattle tannin is classified as a condensed tannin.
Recently, extracts of genus Acacia have been disclosed to have selective inhibitory effects on COX-2 (Patent Document 6), and bark of genus Acacia has been disclosed to have active oxygen removal effects (Patent Document 7) and skin whitening effects due to the effect of inhibiting tyrosinase activity (Patent Document 8).
However, bark of genus Acacia and polyphenols derived from bark thereof have not been known to be able to demonstrate an excellent antioxidative action in the body as a result of being ingested at a specific dose.
[Patent Document 1] JP01-25726A
[Patent Document 2] JP6-65074A
[Patent Document 3] JP7-300422A
[Patent Document 4] JP11-5975A
[Patent Document 5] JP2001-98264A
[Patent Document 6] JP2004-532811A
[Patent Document 7] JP2004-352639A
[Patent Document 8] JP10-025238A